The user resorts to cosmetic reshaping agents to produce curls or to straighten the hair. A long-lasting reshaping of keratinic fibers is normally carried out in such a way that the fibers are mechanically shaped and the shape is set using suitable aids. The fibers are treated with a keratin-reducing preparation before, during, or after this shaping. After a rinsing process, the fiber is then treated in the so-called fixing step with an oxidizing agent preparation, rinsed, and after or during the fixing step freed of shaping aids (e.g., curlers, rollers). If a mercaptan, e.g., ammonium thioglycolate, is used as the keratin-reducing component, part of the disulfide bridges of the keratin molecule is cleaved to —SH groups, resulting in a softening of the keratin fibers. During the later oxidative fixation, disulfide bridges are again formed in the hair keratin, so that the keratin structure is fixed in the given shape. Alternatively, it is known to use sulfite in place of mercaptans for hair shaping. The disulfide bridges of keratin are cleaved by hydrogen sulfite solutions and/or sulfite solutions and/or disulfite solutions in a sulfitolysis according to the equationR—S—S—R+HSO3(−)→R—SH+R—S—SO3(−) and softening of the keratin fibers is achieved in this way. Reducing agents comprising hydrogen sulfite, sulfite, or disulfite do not have the strong characteristic odor of mercaptan-containing agents. The cleavage can be reversed as previously described in a fixing step with the aid of an oxidizing agent with the formation of new disulfide bridges.
The permanent straightening of keratin-containing fibers is achieved similarly by the use of keratin-reducing and keratin-oxidizing compositions. In a suitable method, the curly hair is either wound on curlers with a large diameter of normally more than 15 mm or the hair is combed smooth under the effect of the keratin-reducing composition. Instead of using curlers, it is also possible to straighten the fiber on a straightening board or to straighten the hair by pulling with a comb during the straightening process. Straightening boards are usually rectangular panels, e.g., made of plastic. In so doing, the fiber is preferably wetted with the keratin-reducing preparation.
Another option for straightening hair is straightening with use of a straightening iron after prior application of alkaline products. Such alkaline reshaping agents, in contrast to reshaping with use of keratin-reducing and keratin-oxidizing compositions, do not lead to a conversion of the disulfide bridges, but to a destruction of the disulfide bridges with the formation of monosulfide bridges. Depending on the concentration and application time of the alkaline reshaping agents, protein chains are also cleaved hydrolytically. The pH value of the alkaline reshaping agents is typically in the range of 1-14, preferably of 12-13.
So-called oxidation dyes are used to achieve permanent, intense colors with good fastness properties. Such dyes customarily contain oxidation dye precursors, so-called developer components and coupler components. The developer components form the actual dyes under the influence of oxidizing agents during coupling with one or more coupler components. The oxidation dyes are characterized by intense, excellent, long-lasting coloring results.
If the user desires both a permanent reshaping and coloring of hair, thus the previously described reshaping and coloring methods can be combined. Suitable methods for the simultaneous reshaping and coloring of keratinic fibers have already been described in the literature. Thus, DE 197 13 698 C1 discloses a method in which an oxidation dye precursor and/or a direct dye are added to the oxidizing agent for fixing reshaped hair.
Methods for the simultaneous reshaping and coloring of hair, in which a keratin-reducing preparation is used which already comprises the necessary dyes and/or dye precursors, are known from EP 352 375 A1, EP 1 287 812 A2, and DE 10 2005 061 023 A1.
All these methods known from the prior art are based on the use of a reducing agent and a subsequent fixation by an oxidizing agent, wherein dyes (or dye precursors) are added to either the reducing agent component or, however, to the subsequent used oxidizing agent component.
The reduction of the disulfide bridges in the keratin material, which occurs during the reshaping, is in fact the prerequisite for achieving a satisfactory reshaping effect, but simultaneously also involves the risk of massive hair damage. The cysteine units with disulfide bonds essential for the physical stability of the hair are first cleaved reductively to cysteine, but cannot be restored completely during the subsequent fixation, because part of the cysteine converts to cysteine oxides or cysteic acid in secondary reactions. The hair brought into the malleable state during reshaping thus hardens again by the oxidative fixation and does not resume the original chemical or physical state, however.
After the reshaping treatment, curled, or alternatively straightened, hair results, which is under tension internally, is not in a stable state thermodynamically, comprises new amino acids (such as cysteine oxides and cysteic acid), and is incompletely crosslinked. The user perceives this state as more or less highly pronounced hair damage, which is a general disadvantage of all these reshaping methods, because the use of reducing agents cannot be avoided due to the process.